Castrol Optigear Synthetic PD..ES

Castrol Optigear Synthetic PD..ES collects 7 oils from Castrol in this catalogue. The ISO viscosity grade is the oil's thickness at 40 °C, plus or minus 10 percent. Match the grade the machine manual names before you compare brands. The figures below are the makers' typical values, not a batch certificate. Confirm the current data sheet before you fill a machine. Published viscosity indexes run from 151 to 177. A higher index thins less between 40 °C and 100 °C. That matters in a cold start and in a hot gearbox, and it is not the same thing as the ISO grade. Pour points run from -51 °C to -36 °C. The machine should still start at least 5 °C warmer than the pour point of the oil you pick. 7 are flagged synthetic and 0 are not. Synthetic here means the maker said so. It is not a viscosity grade and it is not, by itself, a reason to leave the ISO grade the manual asks for. None of these rows are tagged PAG. If a data sheet later says polyalkylene glycol, do not mix that oil with a mineral or PAO fill. None of these rows has an Amazon or McMaster-Carr listing in the catalogue yet. The spec comparison is still usable. A distributor quote is the way to buy the rest. Use the table to sort the grade, the viscosity index and the pour point, then open an oil for its data sheet, its equivalents and its buy links. Equivalents on this site are other published oils in the same application and grade. They are not exact substitutes, and the OEM specification still governs.